1. Field of the Invention
The invention relates to a stressing element of fiber composites for prestressed concrete compound units, ground anchors, rock anchors or the like, which has at least one end a stressing or anchoring sleeve which surrounds at a distance at least one stressing bar or a cluster of stressing wires of fiber composites and is filled with a synthetic resin mortar affinitive to the fiber composites, in which mortar the stressing bars or wires are embedded and which mortar establishes the adhesion-shear bond between the latter and the sleeve. The invention also relates to a process and a device for the stressing and anchorage of such a stressing element.
2. Description of the Prior Art
For the prestressing of prestressed concrete compound units, stressing elements with stressing bars or wires of fiber composites have been used recently, which have the advantage over stressing elements with high-strength steel bars or steel wires that they are corrosion-resistant and can also be used in compound units which are exposed to corrosive liquids or gases. Thus, for example, it is expedient to reinforce concrete tanks for liquid chemicals with stressing elements of fiber composites or to use stressing elements of fiber composites for rock or ground anchors which are exposed to ground water. In the case of stressing elements of fiber composites, however, their end anchorage in the concrete of the compound unit presents difficulties, since the stressing bars or clusters of stressing wires of organic or inorganic fibrous materials embedded in a synthetic resin matrix are sensitive to transverse pressure and cannot readily be clamped at the ends and tensioned in the way known with steel bars and also steel wires. In addition, the modulus of elasticity of fiber composites is considerably less than the modulus of elasticity of high-strength steels, so that the stressing elements of fiber composites have to be subjected to a great longitudinal stretching to achieve a sufficiently high prestressing.
An end anchorage for stressing elements of fiber composites is known (European Patent Specification No. 0,025,856), in which the stressing wires of fiber compositions are held between clamping plates, to which a transverse pressure, dependent on the stressing tensile force, is exerted and in which at the same time means are provided such that the clamping pressure does not rise too high, in order to keep the transverse pressure exerted on the stressing wires within allowable limits.
In order to grip stressing bars or stressing wires of fiber composites at their ends without damaging them and to apply a stressing force, it is also already known to house the ends of the stressing bars in sturdy cylindrical stressing or anchoring sleeves, where they are embedded in a synthetic resin mortar, which establishes an adhesion-shear bond between the stressing bars and the stressing or anchoring sleeve. In order to transfer the stressing forces introduced into the stressing sleeve by the stressing press onto the stressing bars or stressing wires of fiber composites embedded in the stressing sleeve, a large anchorage length is required, meaning that the rigid stressing or anchoring sleeves have a large length. This in turn hampers the winding-up of the stressing elements prefabricated at the works onto the stressing element drums, which are used for the transportation of the stressing elements to the construction site.
Above all, however, both known types of anchorage have the disadvantage that the fatigue strength of the stressing elements is inadequate at the points where the stressing bars or stressing elements of fiber composites enter between the clamping plates or into the stressing sleeve of the anchorage.